According to Retronaut, these images show diving suit designs from Hans Talhoffer’s 1459 book Alte Armatur und Ringkunst. I can’t confirm that, but I can confirm that Talhoffer’s classic text on the European martial arts contained images of diving suits.

Talhoffer was a German fencing master. His book, which survives to this day, is a marvel of martial arts instruction in an age of longswords and heavy armor. It continues to inspire martial artists to this day.

The book contained images of various war machines, both real and imagined by Tolhoffer. Do you need to attack an enemy by stealth through the water? Then you need a diving suit like one of these.